The present invention is directed to a system for anchoring a telephone handset to a telephone housing such as the housing for a public or "pay" telephone. Systems for anchoring handsets to such telephone housings are known. See U.S. Pat. No. 4,518,830 (Drexler et al). In such a system, a 3/32 inch diameter 7.times.19 stranded cable having a tensile strength of 800 pounds or more is used to mechanically connect the handset to the housing. The stranded cable is flexible and, together with the signal wires, is sheathed in flexible telephone cord armor ("tca") between the handset and the housing. An end portion of the tca extends within the handset through a grommet and the depending legs of the handset transmitter cup. The stranded cable extends through the yoke of the handset past the junction of the yoke and handset receiver portion. The end of the stranded cable is provided with an end plug or stop. The stranded cable is anchored at the yoke-receiver junction by a wedge-shaped anchor member. See FIGS. 9-11 of the patent. The bottom surface of the anchor member is flat and contacts a relatively flat interior surface of the handset. The top surface of the anchor member is also flat as are the side surfaces of the anchor member. The top surface of the anchor member is disposed at an acute angle with respect to its bottom surface, the two surfaces converging towards the yoke-receiver junction. The stranded cable extends through a slot formed in the bottom surface of the anchor member. The cable end stop is received in a bore in the rear surface of the anchor member. The bore and slot intersect at a shoulder which serves as a stop surface for the cable end stop. Because the top and side surfaces of the anchor member are flat, the surfaces intersect along relatively sharp edges. The interior surface of the handset which faces the top surface of the anchor member is not flat but, instead, comprises a compound surface at the yokereceiver junction. The compound surface is defined by two radii of curvature, one along the longitudinal axis of the handset and the other substantially perpendicular thereto along the width of the handset. The relatively sharp edges of the anchor member make "point" contact with the interior compound surface of the handset. As a result, when the handset is pulled away from the telephone housing, the stranded cable end stop contacts the anchor member shoulder, forcing the relatively sharp edges of the anchor member into "point" contact against the interior compound surface of the handset. At forces substantially less than 800 pounds, the anchor member edges tend to shear or slice through the interior surface of the handset thereby rupturing the handset wall at the yoke-receiver junction.
In the anchoring system employed in U.S. Pat. No. 4,518,830, the handset end of the tca is crimped so as to fit between the transmitter cup legs. The legs and an interior surface of the transmitter end of the handset retain the tca in position. If the spacing between the transmitter cup legs exceeds the outer diameter of the tca, they will not anchor the tca against longitudinal displacement. Thus, when the handset is pulled away from the telephone housing, the handset end of the tca is forced against the grommet. If the handset is pulled with sufficient force, the tca may be forced through and pulled out of the grommet. Likewise, the handset end of the tca may be pushed through the transmitter end of the handset into an acoustic foam block at the junction of the handset transmitter and yoke portions. One problem solved by the present invention is that of anchoring the stranded cable at the yoke-receiver junction of the handset without danger of rupture of the junction wall when forces up to the 800 pound tensile strength of the stranded cable are applied. Another problem solved by the present invention is that of anchoring the handset end of the tca against longitudinal and rotational displacement in the transmitter end of the handset.
The invention includes the discovery that rupture of the handset wall at the yoke-receiver junction is due to "point" contact between the relatively sharp edges of the conventional wedge-shaped anchor member and the compound interior surface of the handset at the yoke-receiver junction. The invention also includes recognition of the inability of the transmitter cup legs to reliably anchor the handset end of the tca in position against longitudinal and rotational displacement at the transmitter end of the handset.
In my invention, the anchor member is shaped so as to have a top compound surface matching the shape of the compound interior surface of the handset at the yoke-receiver junction such that full surface contact is maintained between the anchor member and the handset interior compound surface at the yoke-receiver junction. Such contact distributes the forces produced when the handset is pulled away from the telephone housing so that the forces cannot concentrate at a "point" or even along a "line" thereby preventing rupture of the handset wall at the junction. In addition, in my invention, the handset end of the tca is positively anchored against longitudinal and rotational displacement by a retainer member mounted on the tca and sandwiched between the grommet and transmitter cup legs.
Other advantages of the invention are described hereafter.